With the increase in concern about environmental issues, the demands on automobiles for better fuel economy have been increasing in recent years. Better fuel economy is also being required of rubber compositions used for automotive tires. For example, rubber compositions containing a conjugated diene polymer (e.g., polybutadiene, butadiene-styrene copolymer) and a filler (e.g., carbon black, silica) are used for automotive tires.
An example of a method for improving the fuel economy is proposed in Patent Literature 1; this method uses a diene rubber (modified rubber) that is modified by an organosilicon compound containing an amino group and an alkoxy group. Although the use of a modified rubber improves the fuel economy, it also tends to increase the Mooney viscosity to thereby deteriorate the processability. Moreover, wet-grip performance and abrasion resistance, which are also properties required of rubber compositions used for automotive tires, generally assume an inverse relationship with fuel economy. Thus, it has been difficult to achieve these properties at high levels in a balanced manner.